The present invention is directed to the field of air turbine motor assemblies, particularly those used for applications requiring high volume and low pressure (HVLP) e.g. paint sprayers and the like. In typical previous HVLP applications, it is common to use a modified vacuum cleaner motor design to create the desired air flow. However, vacuum cleaners require large volume air flow, and such motors are designed for large orifices, such as shop vac hoses and attachments. When such vacuum cleaner motors are coupled to HVLP spray guns having small hose diameters, internal passages and orifices, the resulting flow is significantly decreased, in accordance with the principles of fluid mechanics. Such motors typically operate well outside the range of desirable operating conditions, even at less than 10% efficiency.
In addition to the above-noted efficiency losses, the decreased flow in previous systems creates a back pressure which raises the temperature of the air turbine, causing an increase in charge air temperature to the spray gun, heating up the air hose and even adversely affecting the spray pattern. Some previous systems include a separate cooling fan to draw cooling air over the motor during operation. However, a separate cooling fan alone is not sufficient to cool the charge air to the desired temperature.